The invention relates generally to the field of in vivo chemometric analyses of chemical components of cells, tissues, or organs in a living organism.
Analyses of the chemical composition of blood and other tissues are among the most commonly performed medical diagnostic techniques. Typically, such analyses are performed by obtaining a sample of the tissue to be analyzed from a patient (e.g., by drawing blood or by performing a biopsy) and thereafter subjecting the sample to various analytical techniques. Such invasive techniques have disadvantages including discomfort to the patient during sample collection, inconvenience of sample collection, and the possibility that collected samples can be lost or misidentified. Discomfort and inconvenience are magnified in situations in which frequent or regular sample collection is required, such as with blood glucose determinations for diabetic patients.
Various analytical chemical techniques are known for quantitation of individual chemical species, but most such techniques quantify only one or a few chemical species independently or one at a time. Among other analytical techniques that are known are a variety of spectral techniques, including those involving absorbance, transmittance, reflectance, emission, and scattering (elastic and non-elastic) of radiation applied to a sample. For example, Raman scattering analysis of whole blood has been described (Enejder et al., 2002, Optics Lett. 27(22):2004-2006) and is suitable for clinical quantitation of blood glucose, dissolved oxygen, dissolved carbon dioxide, urea, lactic acid, creatine, bicarbonate, electrolytes, protein, albumin, cholesterol, triglycerides, hematocrit, and hemoglobin. Spectral techniques, such as Raman spectral analysis, have the advantage that multiple chemical species can be quantified simultaneously, so long as the species can be spectrally distinguished.
Others have described analytical devices and techniques intended for non-invasive in vivo analysis of tissue components. However, each of these has certain disadvantages and limitations. For example, each of Berger et al. (U.S. Pat. No. 5,615,673) and Yang et al. (U.S. Pat. No. 6,167,290) describes a Raman spectroscopic system designed for transdermal analysis of blood components. Xie (U.S. Patent Application Publication No. 2005/0043597) describes a spectral analysis system intended to analyze blood components using radiation passed across a nail of a finger or toe. In each of these instances, individual variation in skin or nail properties and in blood vessel placement can significantly affect the utility of the devices and methods.
A need exists for systems and methods for non-invasive compositional analysis of human tissues, particularly including blood. The present invention satisfies this need.